The present invention relates generally to an apparatus and method for cooling an air conditioner system in order to boost the efficiency thereof. In order to better understand the invention, some background on the operation of an air conditioner system may be helpful.
Willis Haviland Carrier developed the first modern air conditioning system in 1902. It was designed to solve a humidity problem at the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, N.Y. Paper stock at the plant would sometimes absorb moisture from the warm summer air, making it difficult to apply the layered inking techniques of the time. Carrier treated the air inside the building by blowing it across chilled pipes. The air cooled as it passed across the cold pipes, and since cool air cannot carry as much moisture as warm air, the process reduced the humidity in the plant and stabilized the moisture content of the paper. Reducing the humidity also had the side benefit of lowering the air temperature, and a new technology was born.
The actual process air conditioners use to reduce the ambient air temperature in a room is based on a simple scientific principle. The rest is achieved with the application of a few clever mechanical techniques. Air conditioners use refrigeration to chill indoor air, taking advantage of a physical law—when a liquid converts to a gas (in a process called phase conversion), it absorbs heat. Air conditioners exploit this feature of phase conversion by forcing special chemical compounds to evaporate and condense over and over again in a closed system of coils.
The compounds involved are refrigerants that have properties enabling them to change at relatively low temperatures. Air conditioners also contain fans that move warm interior air over these cold, refrigerant-filled coils. In fact, central air conditioners have a whole system of ducts designed to funnel air to and from these serpentine, air-chilling coils.
When hot air flows over the cold, low-pressure evaporator coils, the refrigerant inside absorbs heat as it changes from a liquid to a gaseous state. To keep cooling efficiently, the air conditioner has to convert the refrigerant gas back to a liquid again. To do that, a compressor puts the gas under high pressure, which is a process that creates unwanted heat. All the extra heat created by compressing the gas is then evacuated to the outdoors with the help of a second set of coils called condenser coils, and a second fan. As the gas cools, it changes back to a liquid, and the process starts all over again. The process can be thought of as an endless cycle: liquid refrigerant, phase conversion to a gas, heat absorption, compression, and phase transition back to a liquid again.
The major parts of an air conditioner manage refrigerant and move air in two directions: indoors and outside. The parts consist of:
Evaporator—Receives the liquid refrigerant;
Condenser—Facilitates heat transfer;
Expansion valve—regulates refrigerant flow into the evaporator;
Compressor—A pump that pressurizes refrigerant.
The cold side of an air conditioner contains the evaporator and a fan that blows air over the chilled coils and into the room. The hot side contains the compressor, condenser, and another fan to vent hot air coming off the compressed refrigerant to the outdoors. In between the two sets of coils, there typically is an expansion valve. It regulates the amount of compressed liquid refrigerant moving into the evaporator. Once in the evaporator, the refrigerant experiences a pressure drop, expands, and changes back into a gas. The compressor typically is an electric pump that pressurizes the refrigerant gas as part of the process of turning it back into a liquid. There are some additional sensors, timers and valves, but the evaporator, compressor, condenser, and expansion valve are the main components of an air conditioner.
Most air conditioners have their capacity rated in British thermal units (Btu). A Btu is the amount of heat necessary to raise the temperature of 1 pound (0.45 kilograms) of water one degree Fahrenheit (0.56 degrees Celsius). One Btu equals 1,055 joules. In heating and cooling terms, one ton equals 12,000 Btu.
A typical window unit air conditioner might be rated at 10,000 Btu. For comparison, a typical 2,000-square-foot (185.8 square meters) house might have a 5-ton (60,000-Btu) air conditioning system, implying that a person might need perhaps 30 Btu per square foot. These are rough estimates. The energy efficiency rating (EER) of an air conditioner is its Btu rating over its wattage. As an example, if a 10,000-Btu air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 Btu/1,200 watts). Obviously, one would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price.
The following example helps illustrate the process of selecting the most economical/efficient air conditioning system. Suppose you have a choice between two 10,000-Btu units. One has an EER of 8.3 and consumes 1,200 watts, and the other has an EER of 10 and consumes 1,000 watts. Suppose also that the price difference between the two units is $100. To determine the payback period on the more expensive unit, you need to know approximately how many hours per year you will be operating the air conditioner and how much a kilowatt-hour (kWh) costs in your area. Assume you plan to use the air conditioner six hours a day for four months of the year, at a cost of $0.10/kWh. The difference in energy consumption between the two units is 200 watts. This means that every five hours the less expensive unit will consume one additional kWh (or $0.10) more than the more expensive unit.
With roughly 30 days in a month, you are operating the air conditioner:
4 months×30 days per month×6 hours per day=720 hours
[(720 hours×200 watts)/(1000 watts/kilowatt)]×$0.10/kilowatt hours=$14.40
The more expensive air conditioning unit costs $100 more to purchase but less money to operate. In our example, it will take seven years (7×$14.40=$100.80) for the higher priced unit to break even. Because of the rising costs of electricity and a growing trend to “go green,” more people are turning to alternative cooling methods to spare their pocketbooks and the environment. Nevertheless, as the above description shows, substantial savings can also be had by increasing the efficiency of an existing air conditioner unit. One way of doing that is by employing the method and apparatus of the present invention, which uses less energy to achieve the same or greater performance.